1. Field of the Invention
The present invention relates to a magnetic field measurement method and a magnetic sensor.
2. Related Background Art
Magnetic sensors which employ a magneto-resistive effect element such as a GMR (Giant Magneto-Resistive) element are known. These magnetic sensors utilize a phenomenon whereby the resistance value of the magneto-resistive effect element depends on the relative angle between the magnetization orientations of a magnetization-free layer and a magnetization fixed layer respectively in the magneto-resistive effect element. More specifically, while a fixed sensing current is flowing in the magneto-resistive effect element, an external magnetic field which is to be measured is applied to the magnetization-free layer in the magnetic sensor in order to change the magnetization direction thereof and measurement of the external magnetic field is performed by measuring the resistance value of the magneto-resistive effect element.
In cases where an external magnetic field is applied to the magnetization-free layer, hysteresis exists for the relationship between the degree of magnetization of the magnetization free layer and the external magnetic field (called ‘hysteresis of the magnetization free layer’ hereinbelow). Hence, hysteresis also exists for the relationship between the resistance value of the magneto-resistive effective element and the external magnetic field (called ‘hysteresis of the element resistance’ hereinbelow). That is, even when an external magnetic field of the same strength is applied, the resistance value and the gain of the magneto-resistive effect element (the gradient of the graph of the external magnetic field/the resistance value of the magneto-resistive effect element) sometimes change depending on the strength of another external magnetic field applied to the magnetization-free layer just before the external magnetic field is applied. When this arises, an error is generated upon measuring the external magnetic field using the magnetic sensor.
In order to reduce such errors, in a conventional magnetic sensor, the magnetization direction of the magnetization fixed layer is fixed in a direction perpendicular to the longitudinal direction of the magnetization fixed layer (see Japanese Patent Application Laid-open No. 2006-19383, for example). The hysteresis of the magnetization fixed layer is accordingly small and therefore errors when measuring an external magnetic field are reduced.